Securing the future of our coastline
Securing the future of our coastline
What is the current state of our metropolitan beaches?
Adelaide essentially has one long beach running 28 kilometres from Kingston Park to Outer Harbor. Our beaches are constantly changing and sand is naturally moved northward by the wind and waves, which causes sand to build up on our northern beaches, such as Semaphore, but causes erosion along our southern and central coast such as Seacliff, Brighton and Henley Beach.
The beaches in the southern part of the coast (from Glenelg to Kingston Park) are generally stable.
From Henley Beach to the north, the beaches are in good condition as the sand lost from southern beaches drifts north. Sand continues to accumulate in Largs Bay, with wide dunes from around the Semaphore jetty northwards.
West Beach has suffered serious and ongoing erosion for a number of years. At present, beach levels at West Beach and Henley Beach south are lower than at any other time since records began.
What has been the impact of our eroded beaches?
The erosion at West Beach has had a number of impacts. Immediately north of the boat harbour the dunes have receded many metres, relying on regular recycling of sand from further north to manage the erosion.
Further north, the beach at the West Beach Surf Life Saving club has been mostly lost and the clubhouse, coast park and car park rely on a seawall for protection.
At the northern end of the seawall, the erosion has lowered the beach so that the beach access ramp is sometimes closed. The loss of dunes in this area has placed assets at risk, and is requiring regular beach replenishment with sand from Semaphore South to maintain protection levels.
The erosion has progressed to affect Henley Beach South, with much of the sand dunes in front of the seawall being recently lost.
What is the DHI report? What does it say?
The Danish Hydraulics Institute (DHI) has completed a report on West Beach coastal processes modelling: assessment of coastal management options. The report was commissioned by the Department for Environment and Water, the Coast Protection Board, the City of Charles Sturt and West Beach Parks.
At West Beach (the section of coastline running north from the West Beach boat harbor at West Beach Parks to the Torrens Outlet), the loss of sand each year is significant, and the new research undertaken by DHI has shown that it is greater than previously estimated.
The report makes it clear that even if current management activities are maintained, erosion will continue around West Beach and Henley Beach South, and progressively move north.
The report tested out three alternative scenarios for managing the beach and dune erosion at West Beach, with their results modelled. All three options involve beach replenishment, and varied by bringing in differing amounts of sand over different timescales. A fourth option – do nothing – does not help the situation.
Feedback from local government, industry and community stakeholders, together with the best available research and modelling has been taken into consideration in final decision making.
Who commissioned the DHI report and why?
In 2017, the Department for Environment and Water commissioned the coastal processes modelling study in order to better understand the coastal processes at West Beach and to examine alternative management options. This was needed because of the ongoing loss of sand each year at West Beach. Following a competitive tender process, DHI was commissioned to undertake the study.
During the course of the study, the scope was amended to expand the analysis of beach profiles along the entire system from Kingston Park to Largs Bay, to enable a better understanding of the influence of management of adjacent beaches on West Beach and vice versa. This expanded analysis also provides insight into the management of the entire Adelaide beach system.
What is the government doing to address the problems in the long term?
The government is investing $48.4 million to the metropolitan coast over four years. This consists of $20 million for additional sand including approximately 500,000 cubic metres (m³) of newly sourced sand; and $28.4 million for the completion of a sand recycling pipeline from Semaphore to West Beach, as well as sand dune restoration and revegetation in partnership with local councils and coastal community groups.
The beach replenishment will put sand on our most vulnerable and eroded beaches including West Beach and Henley Beach South, with benefits to other beaches as sand moves northward.
The announcement has been informed by research completed in 2018 by external consultants the Danish Hydraulics Institute (DHI) on behalf of the Department for Environment and Water, the Coast Protection Board, the City of Charles Sturt and West Beach Parks.
When will it start? When will the pipeline be built?
In 2019/20 and 2020/21, we’ll be increasing our beach replenishment to West Beach and Henley Beach South each year to match current rates of loss and stabilise and maintain the beaches and dunes in the short term.
Then in 2021/22, a large scale replenishment using sand from an external source is planned to be delivered. This will raise the beach levels and boost sand dune buffers at West Beach and Henley Beach South with benefits to other beaches as sand moves northward.
Following the development of plans and logistics specification, the pipeline is planned for construction in 2021/22, with the pipeline operational by end 2022/23.
Where will the sand come from and why do we need an ‘external’ sand source?
There is a limited amount of sand in Adelaide’s beach system and to find a suitable external sand source for the large scale beach replenishment, we will investigate offshore sand deposits at Port Stanvac as well as some land-based sources.
Sand will also continue to be carted by truck from Adelaide’s northern beaches (including the Semaphore South breakwater) in years 2019/20 and 2020/21 to restore sand that is currently being lost from West Beach and Henley Beach South each year while external sand is sourced and the sand recycling pipeline is constructed.
Watch the video to learn more about how we manage Adelaide’s beaches [link to video]
How will this impact our northern beaches, like Semaphore?
Management of the entire metropolitan coast needs to be adaptive and flexible, as our beaches are constantly changing and sand is naturally moved northward by the wind and waves, which causes sand to build up on our northern beaches, such as Semaphore, but causes erosion along our southern and central coast such as Seacliff, Brighton and Henley Beach.
A sustainable approach to managing our beaches will involve recycling sand from areas of where sand builds up to areas of loss. Investigations will take place to see if sand in other northern beaches is suitable to use for beach replenishment while the pipeline is built and before sand from an external source is available.
Using the northern beaches as a sand source will reduce the build-up of sand in the area and some erosion in response to this will occur. The collection areas will be monitored to ensure the foreshore remains protected.
Why are we building a sand recycling pipeline and where will it be located?
A sand recycling pipeline from Semaphore to West Beach will provide an efficient means to recycle sand. This will provide a long term solution to keeping sand on our most exposed and vulnerable beaches.
Pipelines provide more flexibility in managing our beaches – with multiple intake and discharge locations allowing sand to be picked up where there is an accumulation and delivered to locations most at need across the beach system. We have seen this success with the Glenelg to Kingston Park pipeline.
Another major benefit of the pipeline is reducing the use of trucks for sand recycling, making it safer for the community, as well as reducing noise, congestion and the impact of trucks on roads.
The exact location of the pipeline and how it will be built will be determined in the planning and design period starting in 2019-20.
What impacts will building the pipeline have on our beaches and dunes?
We will minimise the impacts as much as possible during construction. The community will be kept informed and have opportunities to find out more in the coming months.
There will be short-term impacts from construction as the pipes will be buried either along the tops of seawalls or at their base, or even deep at the top of the beach. Disturbance of existing dunes and ecological communities will be minimised and disturbance of key areas will be avoided. Any disturbance will be remediated.
The works will add large amounts of sand to the beach system and recycle enough sand each year to maintain critical dune buffers. This provides the base for dune restoration for the foreshore at West Beach and Henley Beach South in particular. The government will partner with the community and councils to revegetate the foreshore and develop stable sand dunes with vibrant ecological communities.
There will be some impact for many residents and beach goers as these works are undertaken. We will keep the community informed during all phases of the projects.
There will be opportunities to find out more in the coming months, including through public events and information sessions. Public notices will be published in local papers and we will also meet with local community groups.
We will work in partnership with local councils and coastal community groups on sand dune restoration and revegetation works.
We will keep the community informed and seek feedback through sessions with key stakeholders and the public.
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How much will the pipeline cost?
The estimated cost is $28.4 million for the completion of a sand recycling pipeline from Semaphore to West Beach as well as sand dune restoration and revegetation to be undertaken in partnership with local councils and coastal community groups.
Don’t we already have a pipeline?
Adelaide’s two existing underground sand recycling pipelines - Glenelg to Kingston Park and Torrens Outlet to the West Beach dunes - were completed in 2013 to transfer a slurry of sand and seawater from beaches where sand is building up, to the eroding beaches further south.
The pipeline from Glenelg to Kingston Park currently pumps approximately 100,000m3 of sand successfully each year.
This project will extend the pipeline from the northern beaches, to connect to the existing infrastructure at Torrens Outlet to the West Beach dunes.
Why is sand being trucked to West Beach when a sand recycling pipeline is already available there?
Sand was trucked or pumped locally from the Torrens Outlet to West Beach and Henley Beach South up until 2018.
However, the 2018 DHI West Beach report determined that large volumes of sand from outside the West Beach area are needed to be brought in to stabilise this section of the coast.
How many trucks will this remove from the roads?
During sand carting there can be between 100-150 truck movements per day on road and streets.
What happened to the sand carted to West Beach over the last year? How is this any different?
The West Beach area has been eroding since the 1960s and has received many hundreds of thousands of cubic metres of sand to manage the area over the years. Previously it was estimated that sand loss from the West Beach area was about 50,000 m³/year. Most of this is through northward movement, with very little lost offshore.
The new research undertaken by DHI estimates that annual losses are actually between two and three times that rate, meaning that even when current replenishment activities are taken into account there is a net annual loss of approximately 60,000 m³.
Windy weather and strong waves have caused erosion to continue at West Beach, and when beaches are replenished with sand it is normal for some of it to be washed away during the next storm. If the replenishment sand wasn’t there, then West Beach would be even more eroded and exposed.
Much of the sand that is washed offshore during storms is washed back onshore during calmer periods, so it is not wasted. This sand will also help maintain beaches as it drifts to the north.
Adding sand to the Adelaide beach system benefits more than just West Beach, it also ensures there is more sand to flow between the beaches and be recycled.
Did the department consider structures like groynes to try to reduce West Beach sand drift north?
By building a structure or structures like groynes and breakwaters that slow sand movement along the coast, the area in the vicinity of the trapped sand can be protected. However, the coast to the north (down-drift) of the structure will then be starved of sand unless the area is replenished.
By focussing on replenishment as the main strategy for protection rather than using structures, the protection of Adelaide’s beaches can be achieved without the additional cost and side effects of expensive structures, which would tend to interrupt our long sandy beaches.
The DHI report does not model any management options that use structures to retain sand on the beaches. Options involving the construction of hard engineering structures to re-orientate the West Beach shoreline were considered by DHI and included offshore breakwaters and headland control structures. A range of risks and disadvantages were identified with these options.
Why does Seacliff beach look so good? How has dune restoration helped?
During the 1980s and 90s, the Seacliff and Brighton coast was suffering from severe erosion that threatened the foreshore. To address this a large scale beach replenishment with sand sourced externally was undertaken. This formed and stabilised the dunes, with the active involvement of local community dune care groups and volunteers. The local council supported these efforts with ongoing restoration involving drift fencing trapping sand to control sand drift, access control, weed removal and re-vegetation. The operation of the sand recycling pipeline from 2013 onwards has further stabilised this part of the coast and allowed dunes to flourish.
What is being done to help beaches outside of Adelaide?
Local councils play a critical role in protecting regional assets from coastal hazards and maintaining coastal areas for all South Australians and tourists. The state government has committed an additional $4 million over 4 years to regional coasts to repair, restore and sustain them in partnership with local councils. This support responds to the increasing demand for coastal protection infrastructure to address hazards like flooding and erosion.
The program will be open to councils with a particular focus on the outer metro and regional areas. Learn more.